Network Working Group H. Shah

Network Working Group H. Shah
Request for Comments: 5041 Broadcom Corporation
Category: Standards Track J. Pinkerton
Microsoft Corporation
R. Recio
IBM Corporation
P. Culley
Hewlett-Packard Company
October 2007

Direct Data Placement over Reliable Transports

Status of This Memo

This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.

Abstract

The Direct Data Placement protocol provides information to Place the
incoming data directly into an upper layer protocol's receive buffer
without intermediate buffers. This removes excess CPU and memory
utilization associated with transferring data through the
intermediate buffers.

Table of Contents

1. Introduction ....................................................3
1.1. Architectural Goals ........................................3
1.2. Protocol Overview ..........................................4
1.3. DDP Layering ...............................................6
2. Glossary ........................................................7
2.1. General ....................................................7
2.2. LLP ........................................................9
2.3. Direct Data Placement (DDP) ................................9
3. Reliable Delivery LLP Requirements .............................12
4. Header Format ..................................................13
4.1. DDP Control Field .........................................13
4.2. DDP Tagged Buffer Model Header ............................14
4.3. DDP Untagged Buffer Model Header ..........................16
4.4. DDP Segment Format ........................................17
5. Data Transfer ..................................................18
5.1. DDP Tagged or Untagged Buffer Models ......................18
5.1.1. Tagged Buffer Model ................................18

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RFC 5041 DDP Protocol Specification October 2007

5.1.2. Untagged Buffer Model ..............................18
5.2. Segmentation and Reassembly of a DDP Message ..............19
5.3. Ordering Among DDP Messages ...............................21
5.4. DDP Message Completion and Delivery .......................21
6. DDP Stream Setup and Teardown ..................................22
6.1. DDP Stream Setup ..........................................22
6.2. DDP Stream Teardown .......................................22
6.2.1. DDP Graceful Teardown ..............................22
6.2.2. DDP Abortive Teardown ..............................23
7. Error Semantics ................................................24
7.1. Errors Detected at the Data Sink ..........................24
7.2. DDP Error Numbers .........................................25
8. Security Considerations ........................................26
8.1. Protocol-Specific Security Considerations .................26
8.2. Association of an STag and a DDP Stream ...................26
8.3. Security Requirements .....................................27
8.3.1. RNIC Requirements ..................................28
8.3.2. Privileged Resources Manager Requirement ...........29
8.4. Security Services for DDP .................................30
8.4.1. Available Security Services ........................30
8.4.2. Requirements for IPsec Services for DDP ............30
9. IANA Considerations ............................................31
10. References ....................................................32
10.1. Normative References .....................................32
10.2. Informative References ...................................33
Appendix A. Receive Window Sizing ................................34
Appendix B. Contributors .........................................34

Table of Figures

Figure 1: DDP Layering ............................................6
Figure 2: MPA, DDP, and RDMAP Header Alignment ....................7
Figure 3: DDP Control Field ......................................13
Figure 4: Tagged Buffer DDP Header ...............................15
Figure 5: Untagged Buffer DDP Header .............................16
Figure 6: DDP Segment Format .....................................17

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RFC 5041 DDP Protocol Specification October 2007

1. Introduction

Note: The capitalization of certain words in this document indicates
they are being used with the specific meaning given in the glossary
(Section 2).

Direct Data Placement Protocol (DDP) enables an Upper Layer Protocol
(ULP) to send data to a Data Sink without requiring the Data Sink to
Place the data in an intermediate buffer - thus, when the data
arrives at the Data Sink, the network interface can Place the data
directly into the ULP's buffer. This can enable the Data Sink to
consume substantially less memory bandwidth than a buffered model
because the Data Sink is not required to move the data from the
intermediate buffer to the final destination. Additionally, this can
enable the network protocol to consume substantially fewer CPU cycles
than if the CPU was used to move the data, and this can remove the
bandwidth limitation of only being able to move data as fast as the
CPU can copy the data.

DDP preserves ULP record boundaries (messages) while providing a
variety of data transfer mechanisms and completion mechanisms to be
used to transfer ULP messages.

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].

1.1. Architectural Goals

DDP has been designed with the following high-level architectural
goals:

* Provide a buffer model that enables the Local Peer to Advertise
a named buffer (i.e., a Tag for a buffer) to the Remote Peer,
such that across the network the Remote Peer can Place data into
the buffer at Remote-Peer-specified locations. This is referred
to as the Tagged Buffer Model.

* Provide a second receive buffer model that preserves ULP message
boundaries from the Remote Peer and keeps the Local Peer's
buffers anonymous (i.e., Untagged). This is referred to as the
Untagged Buffer Model.

* Provide reliable, in-order Delivery semantics for both Tagged
and Untagged Buffer Models.

* Provide segmentation and reassembly of ULP messages.

Shah, et al. Standards Track [Page 3]

RFC 5041 DDP Protocol Specification October 2007

* Enable the ULP Buffer to be used as a reassembly buffer, without
a need for a copy, even if incoming DDP Segments arrive out of
order. This requires the protocol to separate Data Placement of
ULP Payload contained in an incoming DDP Segment from Data
Delivery of completed ULP Messages.

* If the Lower Layer Protocol (LLP) supports multiple LLP Streams
within an LLP Connection, provide the above capabilities
independently on each LLP Stream and enable the capability to be
exported on a per-LLP-Stream basis to the ULP.

1.2. Protocol Overview

DDP supports two basic data transfer models - a Tagged Buffer data
transfer model and an Untagged Buffer data transfer model.

The Tagged Buffer data transfer model requires the Data Sink to send
the Data Source an identifier for the ULP Buffer, referred to as a
Steering Tag (STag). The STag is transferred to the Data Source
using a ULP-defined method. Once the Data Source ULP has an STag for
a destination ULP Buffer, it can request that DDP send the ULP data
to the destination ULP Buffer by specifying the STag to DDP. Note
that the Tagged Buffer does not have to be filled starting at the
beginning of the ULP Buffer. The ULP Data Source can provide an
arbitrary offset into the ULP Buffer.

The Untagged Buffer data transfer model enables data transfer to
occur without requiring the Data Sink to Advertise a ULP Buffer to
the Data Source. The Data Sink can queue up a series of receive ULP
Buffers. An Untagged DDP Message from the Data Source consumes an
Untagged Buffer at the Data Sink. Because DDP is message oriented,
even if the Data Source sends a DDP Message payload smaller than the
receive ULP Buffer, the partially filled receive ULP Buffer is
delivered to the ULP anyway. If the Data Source sends a DDP Message
payload larger than the receive ULP Buffer, it results in an error.

There are several key differences between the Tagged and Untagged
Buffer Model:

* For the Tagged Buffer Model, the Data Source specifies which
received Tagged Buffer will be used for a specific Tagged DDP
Message (sender-based ULP Buffer management). For the Untagged
Buffer Model, the Data Sink specifies the order in which
Untagged Buffers will be consumed as Untagged DDP Messages are
received (receiver-based ULP Buffer management).

* For the Tagged Buffer Model, the ULP at the Data Sink must
Advertise the ULP Buffer to the Data Source through a ULP

Shah, et al. Standards Track [Page 4]

RFC 5041 DDP Protocol Specification October 2007

specific mechanism before data transfer can occur. For the
Untagged Buffer Model, data transfer can occur without an end-
to-end explicit ULP Buffer Advertisement. Note, however, that
the ULP needs to address flow control issues.

* For the Tagged Buffer Model, a DDP Message can start at an
arbitrary offset within the Tagged Buffer. For the Untagged
Buffer Model, a DDP Message can only start at offset 0.

* The Tagged Buffer Model allows multiple DDP Messages targeted to
a Tagged Buffer with a single ULP Buffer Advertisement. The
Untagged Buffer Model requires associating a receive ULP Buffer
for each DDP Message targeted to an Untagged Buffer.

Either data transfer model Places a ULP Message into a DDP Message.
Each DDP Message is then sliced into DDP Segments that are intended
to fit within a lower-layer-protocol's (LLP) Maximum Upper Layer
Protocol Data Unit (MULPDU). Thus, the ULP can post arbitrarily
sized ULP Messages, containing up to 2^32 - 1 octets of ULP Payload,
and DDP slices the ULP message into DDP Segments, which are
reassembled transparently at the Data Sink.

DDP provides in-order delivery for the ULP. However, DDP
differentiates between Data Delivery and Data Placement. DDP
provides enough information in each DDP Segment to allow the ULP
Payload in each inbound DDP Segment payloads to be directly Placed
into the correct ULP Buffer, even when the DDP Segments arrive out-
of-order. Thus, DDP enables the reassembly of ULP Payload contained
in DDP Segments of a DDP Message into a ULP Message to occur within
the ULP Buffer, therefore eliminating the traditional copy out of the
reassembly buffer into the ULP Buffer.

A DDP Message's payload is Delivered to the ULP when:

* all DDP Segments of a DDP Message have been completely received,
and the payload of the DDP Message has been Placed into the
associated ULP Buffer,

* all prior DDP Messages have been Placed, and

* all prior DDP Message Deliveries have been performed.

The LLP under DDP may support a single LLP Stream of data per
connection (e.g., TCP [TCP]) or multiple LLP Streams of data per
connection (e.g., SCTP [SCTP]). But in either case, DDP is specified
such that each DDP Stream is independent and maps to a single LLP
Stream. Within a specific DDP Stream, the LLP Stream is required to

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provide in-order, reliable Delivery. Note that DDP has no ordering
guarantees between DDP Streams.

A DDP protocol could potentially run over reliable Delivery LLPs or
unreliable Delivery LLPs. This specification requires reliable, in
order Delivery LLPs.

1.3. DDP Layering

DDP is intended to be LLP independent, subject to the requirements
defined in section 3. However, DDP was specifically defined to be
part of a family of protocols that were created to work well
together, as shown in Figure 1, DDP Layering. For LLP protocol
definitions of each LLP, see Marker PDU Aligned Framing for TCP
Specification [MPA] and Stream Control Transmission Protocol (SCTP)
Direct Data Placement (DDP) Adaptation [SCTPDDP].

DDP enables direct data Placement capability for any ULP, but it has
been specifically designed to work well with Remote Direct Memory
Access Protocol (RDMAP) (see [RDMAP]), and is part of the iWARP
protocol suite.

+-------------------+
| |
| RDMA ULP |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | |
| ULP | RDMAP |
| | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| DDP protocol |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | |
| MPA | |
| | |
| | |
+-+-+-+-+-+-+-+-+-+ SCTP |
| | |
| TCP | |
| | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 1: DDP Layering

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If DDP is layered below RDMAP and on top of MPA and TCP, then the
respective headers and payload are arranged as follows (Note: For
clarity, MPA header and CRC are included, but framing markers are not
shown.):

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// TCP Header //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MPA Header | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| |
// DDP Header //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// RDMAP Header //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// //
// RDMAP ULP Payload //
// //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MPA CRC |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 2: MPA, DDP, and RDMAP Header Alignment

2. Glossary

2.1. General

Advertisement (Advertised, Advertise, Advertisements, Advertises) -
The act of informing a Remote Peer that a local RDMA Buffer is
available to it. A Node makes available an RDMA Buffer for
incoming RDMA Read or RDMA Write access by informing its RDMA/DDP
peer of the Tagged Buffer identifiers (STag, base address,
length). This Advertisement of Tagged Buffer information is not
defined by RDMA/DDP and is left to the ULP. A typical method
would be for the Local Peer to embed the Tagged Buffer's Steering
Tag, address, and length in a Send message destined for the
Remote Peer.

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RFC 5041 DDP Protocol Specification October 2007

Data Delivery (Delivery, Delivered, Delivers) - Delivery is defined
as the process of informing the ULP or consumer that a particular
message is available for use. This is specifically different
from "Placement", which may generally occur in any order, while
the order of "Delivery" is strictly defined. See "Data
Placement".

Data Sink - The peer receiving a data payload. Note that the Data
Sink can be required to both send and receive RDMA/DDP Messages
to transfer a data payload.

Data Source - The peer sending a data payload. Note that the Data
Source can be required to both send and receive RDMA/DDP Messages
to transfer a data payload.

Delivery (Delivered, Delivers) - See Data Delivery in Section 2.1.

iWARP - A suite of wire protocols comprised of RDMAP [RDMAP], DDP
(this specification), and Marker PDU Aligned Framing for TCP
(MPA) [MPA]. The iWARP protocol suite may be layered above TCP,
SCTP, or other transport protocols.

Local Peer - The RDMA/DDP protocol implementation on the local end of
the connection. Used to refer to the local entity when
describing a protocol exchange or other interaction between two
Nodes.

Node - A computing device attached to one or more links of a network.
A Node in this context does not refer to a specific application
or protocol instantiation running on the computer. A Node may
consist of one or more RDMA Enabled Network Interface Controllers
(RNICs) installed in a host computer.

Placement (Placed, Places) - See "Data Placement" in Section 2.3

Remote Peer - The RDMA/DDP protocol implementation on the opposite
end of the connection. Used to refer to the remote entity when
describing protocol exchanges or other interactions between two
Nodes.

RNIC - RDMA Enabled Network Interface Controller. In this context,
this would be a network I/O adapter or embedded controller with
iWARP functionality.

ULP - Upper Layer Protocol. The protocol layer above the protocol
layer currently being referenced. The ULP for RDMA/DDP is
expected to be an Operating System (OS), application, adaptation
layer, or proprietary device. The RDMA/DDP documents do not

Shah, et al. Standards Track [Page 8]

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specify a ULP -- they provide a set of semantics that allow a ULP
to be designed to utilize RDMA/DDP.

ULP Message - The ULP data that is handed to a specific protocol
layer for transmission. Data boundaries are preserved as they
are transmitted through iWARP.

ULP Payload - The ULP data that is contained within a single protocol
segment or packet (e.g., a DDP Segment).

2.2. LLP

LLP - Lower Layer Protocol. The protocol layer beneath the protocol
layer currently being referenced. For example, for DDP, the LLP
is SCTP DDP Adaptation, MPA, or other transport protocols. For
RDMA, the LLP is DDP.

LLP Connection - Corresponds to an LLP transport-level connection
between the peer LLP layers on two nodes.

LLP Stream - Corresponds to a single LLP transport-level stream
between the peer LLP layers on two Nodes. One or more LLP
Streams may map to a single transport-level LLP Connection. For
transport protocols that support multiple streams per connection
(e.g., SCTP), an LLP Stream corresponds to one transport-level
stream.

MULPDU - Maximum Upper Layer Protocol Data Unit (MULPDU). The
current maximum size of the record that is acceptable for DDP to
pass to the LLP for transmission.

ULPDU - Upper Layer Protocol Data Unit. The data record defined by
the layer above MPA.

2.3. Direct Data Placement (DDP)

Data Placement (Placement, Placed, Places) - For DDP, this term is
specifically used to indicate the process of writing to a Data
Buffer by a DDP implementation. DDP Segments carry Placement
information, which may be used by the receiving DDP
implementation to perform Data Placement of the DDP Segment ULP
Payload. See "Data Delivery" and "Direct Data Placement".

DDP Abortive Teardown - The act of closing a DDP Stream without
attempting to complete in-progress and pending DDP Messages.

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DDP Graceful Teardown - The act of closing a DDP Stream such that all
in-progress and pending DDP Messages are allowed to complete
successfully.

DDP Control Field - A fixed 8-bit field in the DDP Header.

DDP Header - The header present in all DDP Segments. The DDP Header
contains control and Placement fields that are used to define the
final Placement location for the ULP Payload carried in a DDP
Segment.

DDP Message - A ULP-defined unit of data interchange, which is
subdivided into one or more DDP Segments. This segmentation may
occur for a variety of reasons, including segmentation to respect
the maximum segment size of the underlying transport protocol.

DDP Segment - The smallest unit of data transfer for the DDP
protocol. It includes a DDP Header and ULP Payload (if present).
A DDP Segment should be sized to fit within the Lower Layer
Protocol MULPDU.

DDP Stream - A sequence of DDP messages whose ordering is defined by
the LLP. For SCTP, a DDP Stream maps directly to an SCTP stream.
For MPA, a DDP Stream maps directly to a TCP connection, and a
single DDP Stream is supported. Note that DDP has no ordering
guarantees between DDP Streams.

DDP Stream Identifier (ID) - An identifier for a DDP Stream.

Direct Data Placement - A mechanism whereby ULP data contained within
DDP Segments may be Placed directly into its final destination in
memory without processing of the ULP. This may occur even when
the DDP Segments arrive out of order. Out-of-order Placement
support may require the Data Sink to implement the LLP and DDP as
one functional block.

Direct Data Placement Protocol (DDP) - Also, a wire protocol that
supports Direct Data Placement by associating explicit memory
buffer placement information with the LLP payload units.

Message Offset (MO) - For the DDP Untagged Buffer Model, specifies
the offset, in octets, from the start of a DDP Message.

Message Sequence Number (MSN) - For the DDP Untagged Buffer Model,
specifies a sequence number that is increasing with each DDP
Message.

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RFC 5041 DDP Protocol Specification October 2007

Protection Domain (PD) - A mechanism used to associate a DDP Stream
and an STag. Under this mechanism, the use of an STag is valid
on a DDP Stream if the STag has the same Protection Domain
Identifier (PD ID) as the DDP Stream.

Protection Domain Identifier (PD ID) - An identifier for the
Protection Domain.

Queue Number (QN) - For the DDP Untagged Buffer Model, identifies a
destination Data Sink queue for a DDP Segment.

Steering Tag - An identifier of a Tagged Buffer on a Node, valid as
defined within a protocol specification.

STag - Steering Tag

Tagged Buffer - A buffer that is explicitly Advertised to the Remote
Peer through exchange of an STag, Tagged Offset, and length.

Tagged Buffer Model - A DDP data transfer model used to transfer
Tagged Buffers from the Local Peer to the Remote Peer.

Tagged DDP Message - A DDP Message that targets a Tagged Buffer.

Tagged Offset (TO) - The offset within a Tagged Buffer on a Node.

ULP Buffer - A buffer owned above the DDP layer and Advertised to the
DDP layer either as a Tagged Buffer or an Untagged ULP Buffer.

ULP Message Length - The total length, in octets, of the ULP Payload
contained in a DDP Message.

Untagged Buffer - A buffer that is not explicitly Advertised to the
Remote Peer.

Untagged Buffer Model - A DDP data transfer model used to transfer
Untagged Buffers from the Local Peer to the Remote Peer.

Untagged DDP Message - A DDP Message that targets an Untagged Buffer.

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RFC 5041 DDP Protocol Specification October 2007

3. Reliable Delivery LLP Requirements

Any protocol that can serve as an LLP to DDP MUST meet the following
requirements.

1. LLPs MUST expose MULPDU and MULPDU changes. This is required so
that the DDP layer can perform segmentation aligned with the
MULPDU and can adapt as MULPDU changes come about. The corner
case of how to handle outstanding requests during a MULPDU change
is covered by the requirements below.

2. In the event of a MULPDU change, DDP MUST NOT be required by the
LLP to re-segment DDP Segments that have been previously posted
to the LLP. Note that under pathological conditions the LLP may
change the Advertised MULPDU more frequently than the queue of
previously posted DDP Segment transmit requests is flushed.
Under this pathological condition, the LLP transmit queue can
contain DDP Messages for which multiple updates to the
corresponding MULPDU have occurred subsequent to posting of the
messages. Thus, there may be no correlation between the queued
DDP Segment(s) and the LLP's current value of MULPDU.

3. The LLP MUST ensure that, if it accepts a DDP Segment, it will
transfer it reliably to the receiver or return with an error
stating that the transfer failed to complete.

4. The LLP MUST preserve DDP Segment and Message boundaries at the
Data Sink.

5. The LLP MAY provide the incoming segments out of order for
Placement, but if it does, it MUST also provide information that
specifies what the sender-specified order was.

6. LLP MUST provide a strong digest (at least equivalent to CRC32-C)
to cover at least the DDP Segment. It is believed that some of
the existing data integrity digests are not sufficient, and that
direct memory transfer semantics requires a stronger digest than,
for example, a simple checksum.

7. On receive, the LLP MUST provide the length of the DDP Segment
received. This ensures that DDP does not have to carry a length
field in its header.

8. If an LLP does not support teardown of an LLP Stream independent
of other LLP Streams, and a DDP error occurs on a specific DDP
Stream, then the LLP MUST label the associated LLP Stream as an
erroneous LLP Stream and MUST NOT allow any further data transfer

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RFC 5041 DDP Protocol Specification October 2007

on that LLP Stream after DDP requests the associated DDP Stream
to be torn down.

9. For a specific LLP Stream, the LLP MUST provide a mechanism to
indicate that the LLP Stream has been gracefully torn down. For
a specific LLP Connection, the LLP MUST provide a mechanism to
indicate that the LLP Connection has been gracefully torn down.

Note that, if the LLP does not allow an LLP Stream to be torn
down independently of the LLP Connection, the above requirements
allow the LLP to notify DDP of both events at the same time.

10. For a specific LLP Connection, when all LLP Streams are either
gracefully torn down or are labeled as erroneous LLP Streams, the
LLP Connection MUST be torn down.

11. The LLP MUST NOT pass a duplicate DDP Segment to the DDP layer
after it has passed all the previous DDP Segments to the DDP
layer and the associated ordering information for the previous
DDP Segments and the current DDP Segment.

4. Header Format

DDP has two different header formats: one for Data Placement into
Tagged Buffers, and the other for Data Placement into Untagged
Buffers. See Section 5.1 for a description of the two models.

4.1. DDP Control Field

The first 8 bits of the DDP Header carry a DDP Control Field that is
common between the two formats. It is shown below in Figure 3,
offset by 16 bits to accommodate the MPA header defined in [MPA].
The MPA header is only present if DDP is layered on top of MPA.

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+
|T|L| Rsvd |DV |
+-+-+-+-+-+-+-+-+

Figure 3: DDP Control Field

T - Tagged flag: 1 bit.

Specifies the Tagged or Untagged Buffer Model. If set to one,
the ULP Payload carried in this DDP Segment MUST be Placed into a
Tagged Buffer.

Shah, et al. Standards Track [Page 13]

RFC 5041 DDP Protocol Specification October 2007

If set to zero, the ULP Payload carried in this DDP Segment MUST
be Placed into an Untagged Buffer.

L - Last flag: 1 bit.

Specifies whether the DDP Segment is the last segment of a DDP
Message. It MUST be set to one on the last DDP Segment of every
DDP Message. It MUST NOT be set to one on any other DDP Segment.

The DDP Segment with the L bit set to 1 MUST be posted to the LLP
after all other DDP Segments of the associated DDP Message have
been posted to the LLP. For an Untagged DDP Message, the DDP
Segment with the L bit set to 1 MUST carry the highest MO.

If the Last flag is set to one, the DDP Message payload MUST be
Delivered to the ULP after:

o Placement of all DDP Segments of this DDP Message and all
prior DDP Messages, and

o Delivery of each prior DDP Message.

If the Last flag is set to zero, the DDP Segment is an
intermediate DDP Segment.

Rsvd - Reserved: 4 bits.

Reserved for future use by the DDP protocol. This field MUST be
set to zero on transmit, and not checked on receive.

DV - Direct Data Placement Protocol Version: 2 bits.

The version of the DDP Protocol in use. This field MUST be set
to one to indicate the version of the specification described in
this document. The value of DV MUST be the same for all the DDP
Segments transmitted or received on a DDP Stream.

4.2. DDP Tagged Buffer Model Header

Figure 4 shows the DDP Header format that MUST be used in all DDP
Segments that target Tagged Buffers. It includes the DDP Control
Field previously defined in Section 4.1. (Note: In Figure 4, the DDP
Header is offset by 16 bits to accommodate the MPA header defined in
[MPA]. The MPA header is only present if DDP is layered on top of
MPA.)

Shah, et al. Standards Track [Page 14]

RFC 5041 DDP Protocol Specification October 2007

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|T|L| Rsvd | DV| RsvdULP |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| STag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ TO +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 4: Tagged Buffer DDP Header

T is set to one.

RsvdULP - Reserved for use by the ULP: 8 bits.

The RsvdULP field is opaque to the DDP protocol and can be
structured in any way by the ULP. At the Data Source, DDP MUST
set RsvdULP Field to the value specified by the ULP. It is
transferred unmodified from the Data Source to the Data Sink. At
the Data Sink, DDP MUST provide the RsvdULP field to the ULP when
the DDP Message is delivered. Each DDP Segment within a specific
DDP Message MUST contain the same value for this field. The Data
Source MUST ensure that each DDP Segment within a specific DDP
Message contains the same value for this field.

STag - Steering Tag: 32 bits.

The Steering Tag identifies the Data Sink's Tagged Buffer. The
STag MUST be valid for this DDP Stream. The STag is associated
with the DDP Stream through a mechanism that is outside the scope
of the DDP Protocol specification. At the Data Source, DDP MUST
set the STag field to the value specified by the ULP. At the
Data Sink, the DDP MUST provide the STag field when the ULP
Message is delivered. Each DDP Segment within a specific DDP
Message MUST contain the same value for this field and MUST be
the value supplied by the ULP. The Data Source MUST ensure that
each DDP Segment within a specific DDP Message contains the same
value for this field.

TO - Tagged Offset: 64 bits.

The Tagged Offset specifies the offset, in octets, within the
Data Sink's Tagged Buffer, where the Placement of ULP Payload
contained in the DDP Segment starts. A DDP Message MAY start at
an arbitrary TO within a Tagged Buffer.

Shah, et al. Standards Track [Page 15]

RFC 5041 DDP Protocol Specification October 2007

4.3. DDP Untagged Buffer Model Header

Figure 5 shows the DDP Header format that MUST be used in all DDP
Segments that target Untagged Buffers. It includes the DDP Control
Field previously defined in Section 4.1. (Note: In Figure 5, the DDP
Header is offset by 16 bits to accommodate the MPA header defined in
[MPA]. The MPA header is only present if DDP is layered on top of
MPA.)

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|T|L| Rsvd | DV| RsvdULP[0:7] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RsvdULP[8:39] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| QN |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MSN |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MO |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 5: Untagged Buffer DDP Header

T is set to zero.

RsvdULP - Reserved for use by the ULP: 40 bits.

The RsvdULP field is opaque to the DDP protocol and can be
structured in any way by the ULP. At the Data Source, DDP MUST
set RsvdULP Field to the value specified by the ULP. It is
transferred unmodified from the Data Source to the Data Sink. At
the Data Sink, DDP MUST provide RsvdULP field to the ULP when the
ULP Message is Delivered. Each DDP Segment within a specific DDP
Message MUST contain the same value for the RsvdULP field. At
the Data Sink, the DDP implementation is NOT REQUIRED to verify
that the same value is present in the RsvdULP field of each DDP
Segment within a specific DDP Message and MAY provide the value
from any one of the received DDP Segment to the ULP when the ULP
Message is Delivered.

Shah, et al. Standards Track [Page 16]

RFC 5041 DDP Protocol Specification October 2007

QN - Queue Number: 32 bits.

The Queue Number identifies the Data Sink's Untagged Buffer queue
referenced by this header. Each DDP segment within a specific
DDP message MUST contain the same value for this field and MUST
be the value supplied by the ULP at the Data Source. The Data
Source MUST ensure that each DDP Segment within a specific DDP
Message contains the same value for this field.

MSN - Message Sequence Number: 32 bits.

The Message Sequence Number specifies a sequence number that MUST
be increased by one (modulo 2^32) with each DDP Message targeting
the specific Queue Number on the DDP Stream associated with this
DDP Segment. The initial value for MSN MUST be one. The MSN
value MUST wrap to 0 after a value of 0xFFFFFFFF. Each DDP
segment within a specific DDP message MUST contain the same value
for this field. The Data Source MUST ensure that each DDP
Segment within a specific DDP Message contains the same value for
this field.

MO - Message Offset: 32 bits.

The Message Offset specifies the offset, in octets, from the
start of the DDP Message represented by the MSN and Queue Number
on the DDP Stream associated with this DDP Segment. The MO
referencing the first octet of the DDP Message MUST be set to
zero by the DDP layer.

4.4. DDP Segment Format

Each DDP Segment MUST contain a DDP Header. Each DDP Segment may
also contain ULP Payload. Following is the DDP Segment format:

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DDP | |
| Header| ULP Payload (if any) |
| | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 6: DDP Segment Format

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5. Data Transfer

DDP supports multi-segment DDP Messages. Each DDP Message is
composed of one or more DDP Segments. Each DDP Segment contains a
DDP Header. The DDP Header contains the information required by the
receiver to Place any ULP Payload included in the DDP Segment.

5.1. DDP Tagged or Untagged Buffer Models

DDP uses two basic buffer models for the Placement of the ULP
Payload: Tagged Buffer Model and Untagged Buffer Model.

5.1.1. Tagged Buffer Model

The Tagged Buffer Model is used by the Data Source to transfer a DDP
Message into a Tagged Buffer at the Data Sink that has been
previously Advertised to the Data Source. An STag identifies a
Tagged Buffer. For the Placement of a DDP Message using the Tagged
Buffer Model, the STag is used to identify the buffer, and the TO is
used to identify the offset within the Tagged Buffer into which the
ULP Payload is transferred. The protocol used to Advertise the
Tagged Buffer is outside the scope of this specification (i.e., ULP
specific). A DDP Message can start at an arbitrary TO within a
Tagged Buffer.

Additionally, a Tagged Buffer can potentially be written multiple
times. This might be done for error recovery or because a buffer is
being re-used after some ULP specific synchronization mechanism.

5.1.2. Untagged Buffer Model

The Untagged Buffer Model is used by the Data Source to transfer a
DDP Message to the Data Sink into a queued buffer.

The DDP Queue Number is used by the ULP to separate ULP messages into
different queues of receive buffers. For example, if two queues were
supported, the ULP could use one queue to post buffers handed to it
by the application above the ULP, and it could use the other queue
for buffers that are only consumed by ULP-specific control messages.
This enables the separation of ULP control messages from opaque ULP
Payload when using Untagged Buffers.

The DDP Message Sequence Number can be used by the Data Sink to
identify the specific Untagged Buffer. The protocol used to
communicate how many buffers have been queued is outside the scope of
this specification. Similarly, the exact implementation of the
buffer queue is outside the scope of this specification.

Shah, et al. Standards Track [Page 18]

RFC 5041 DDP Protocol Specification October 2007

5.2. Segmentation and Reassembly of a DDP Message

At the Data Source, the DDP layer MUST segment the data contained in
a ULP message into a series of DDP Segments, where each DDP Segment
contains a DDP Header and ULP Payload, and MUST be no larger than the
MULPDU value Advertised by the LLP. The ULP Message Length MUST be
less than 2^32. At the Data Source, the DDP layer MUST send all the
data contained in the ULP message. At the Data Sink, the DDP layer
MUST Place the ULP Payload contained in all valid incoming DDP
Segments associated with a DDP Message into the ULP Buffer.

DDP Message segmentation at the Data Source is accomplished by
identifying a DDP Message (which corresponds one-to-one with a ULP
Message) uniquely and then, for each associated DDP Segment of a DDP
Message, by specifying an octet offset for the portion of the ULP
Message contained in the DDP Segment.

For an Untagged DDP Message, the combination of the QN and MSN
uniquely identifies a DDP Message. The octet offset for each DDP
Segment of a Untagged DDP Message is the MO field. For each DDP
Segment of a Untagged DDP Message, the MO MUST be set to the octet
offset from the first octet in the associated ULP Message (which is
defined to be zero) to the first octet in the ULP Payload contained
in the DDP Segment.

For example, if the ULP Untagged Message was 2048 octets, and the
MULPDU was 1500 octets, the Data Source would generate two DDP
Segments, one with MO = 0, containing 1482 octets of ULP Payload, and
a second with MO = 1482, containing 566 octets of ULP Payload. In
this example, the amount of ULP Payload for the first DDP Segment was
calculated as:

1482 = 1500 (MULPDU) - 18 (for the DDP Header)

For a Tagged DDP Message, the STag and TO, combined with the in-order
delivery characteristics of the LLP, are used to segment and
reassemble the ULP Message. Because the initial octet offset (the TO
field) can be non-zero, recovery of the original ULP Message boundary
cannot be done in the general case without an additional ULP Message.

Implementers' note: One implementation, valid for some ULPs such
as RDMAP, is to not directly support recovery of the ULP Message
boundary for a Tagged DDP Message. For example, the ULP may wish
to have the Local Peer use small buffers at the Data Source even
when the ULP at the Data Sink has Advertised a single large
Tagged Buffer for this data transfer. In this case, the ULP may
choose to use the same STag for multiple consecutive ULP
Messages. Thus, a non-zero initial TO and re-use of the STag

Shah, et al. Standards Track [Page 19]

RFC 5041 DDP Protocol Specification October 2007

effectively enable the ULP to implement segmentation and
reassembly due to ULP-specific constraints. See [RDMAP] for
details of how this is done.

A different implementation of a ULP could use an Untagged DDP
Message (sent after the Tagged DDP Message) that details the
initial TO for the STag that was used in the Tagged DDP Message.
And finally, another implementation of a ULP could choose to
always use an initial TO of zero such that no additional message
is required to convey the initial TO used in a Tagged DDP
Message.

Regardless of whether the ULP chooses to recover the original ULP
Message boundary at the Data Sink for a Tagged DDP Message, DDP
supports segmentation and reassembly of the Tagged DDP Message. The
STag is used to identify the ULP Buffer at the Data Sink, and the TO
is used to identify the octet-offset within the ULP Buffer referenced
by the STag. The ULP at the Data Source MUST specify the STag and
the initial TO when the ULP Message is handed to DDP.

For each DDP Segment of a Tagged DDP Message, the TO MUST be set to
the octet offset from the first octet in the associated ULP Message
to the first octet in the ULP Payload contained in the DDP Segment,
plus the TO assigned to the first octet in the associated ULP
Message.

For example, if the ULP Tagged Message was 2048 octets with an
initial TO of 16384, and the MULPDU was 1500 octets, the Data Source
would generate two DDP Segments: one with TO = 16384, containing the
first 1486 octets of ULP payload, and a second with TO = 17870,
containing 562 octets of ULP payload. In this example, the amount of
ULP payload for the first DDP Segment was calculated as:

1486 = 1500 (MULPDU) - 14 (for the DDP Header)

A zero-length DDP Message is allowed and MUST consume exactly one DDP
Segment. Only the DDP Control and RsvdULP Fields MUST be valid for a
zero-length Tagged DDP Segment. The STag and TO fields MUST NOT be
checked for a zero-length Tagged DDP Message.

For either Untagged or Tagged DDP Messages, the Data Sink is not
required to verify that the entire ULP Message has been received.

Shah, et al. Standards Track [Page 20]

RFC 5041 DDP Protocol Specification October 2007

5.3. Ordering Among DDP Messages

Messages passed through the DDP MUST conform to the ordering rules
defined in this section.

At the Data Source, DDP:

* MUST transmit DDP Messages in the order they were submitted to
the DDP layer,

* SHOULD transmit DDP Segments within a DDP Message in increasing
MO order for Untagged DDP Messages, and in increasing TO order
for Tagged DDP Messages.

At the Data Sink, DDP (Note: The following rules are motivated by LLP
implementations that separate Placement and Delivery.):

* MAY perform Placement of DDP Segments out of order,

* MAY perform Placement of a DDP Segment more than once,

* MUST Deliver a DDP Message to the ULP at most once,

* MUST Deliver DDP Messages to the ULP in the order they were sent
by the Data Source.

5.4. DDP Message Completion and Delivery

At the Data Source, DDP Message transfer is considered completed when
the reliable, in-order transport LLP has indicated that the transfer
will occur reliably. Note that this in no way restricts the LLP from
buffering the data at either the Data Source or Data Sink. Thus, at
the Data Source, completion of a DDP Message does not necessarily
mean that the Data Sink has received the message.

At the Data Sink, DDP MUST Deliver a DDP Message if and only if all
of the following are true:

* the last DDP Segment of the DDP Message had its Last flag set,

* all of the DDP Segments of the DDP Message have been Placed,

* all preceding DDP Messages have been Placed, and

* each preceding DDP Message has been Delivered to the ULP.

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At the Data Sink, DDP MUST provide the ULP Message Length to the ULP
when an Untagged DDP Message is Delivered. The ULP Message Length
may be calculated by adding the MO and the ULP Payload length in the
last DDP Segment (with the Last flag set) of an Untagged DDP Message.

At the Data Sink, DDP MUST provide the RsvdULP Field of the DDP
Message to the ULP when the DDP Message is delivered.

6. DDP Stream Setup and Teardown

This section describes LLP independent issues related to DDP Stream
setup and teardown.

6.1. DDP Stream Setup

It is expected that the ULP will use a mechanism outside the scope of
this specification to establish an LLP Connection, and that the LLP
Connection will support one or more LLP Streams (e.g., MPA/TCP or
SCTP). After the LLP sets up the LLP Stream, it will enable a DDP
Stream on a specific LLP Stream at an appropriate point.

The ULP is required to enable both endpoints of an LLP Stream for DDP
data transfer at the same time, in both directions; this is necessary
so that the Data Sink can properly recognize the DDP Segments.

6.2. DDP Stream Teardown

DDP MUST NOT independently initiate Stream Teardown. DDP either
responds to a stream being torn down by the LLP or processes a
request from the ULP to tear down a stream. DDP Stream teardown
disables DDP capabilities on both endpoints. For connection-oriented
LLPs, DDP Stream teardown MAY result in underlying LLP Connection
teardown.

6.2.1. DDP Graceful Teardown

It is up to the ULP to ensure that DDP teardown happens on both
endpoints of the DDP Stream at the same time; this is necessary so
that the Data Sink stops trying to interpret the DDP Segments.

If the Local Peer ULP indicates graceful teardown, the DDP layer on
the Local Peer SHOULD ensure that all ULP data would be transferred
before the underlying LLP Stream and Connection are torn down, and
any further data transfer requests by the Local Peer ULP MUST return
an error.

Shah, et al. Standards Track [Page 22]

RFC 5041 DDP Protocol Specification October 2007

If the DDP layer on the Local Peer receives a graceful teardown
request from the LLP, any further data received after the request is
considered an error and MUST cause the DDP Stream to be abortively
torn down.

If the Local Peer LLP supports a half-closed LLP Stream, on the
receipt of an LLP graceful teardown request of the DDP Stream, DDP
SHOULD indicate the half-closed state to the ULP, and continue to
process outbound data transfer requests normally. Following this
event, when the Local Peer ULP requests graceful teardown, DDP MUST
indicate to the LLP that it SHOULD perform a graceful close of the
other half of the LLP Stream.

If the Local Peer LLP supports a half-closed LLP Stream, on the
receipt of a ULP graceful half-closed teardown request of the DDP
Stream, DDP SHOULD keep data reception enabled on the other half of
the LLP Stream.

6.2.2. DDP Abortive Teardown

As previously mentioned, DDP does not independently terminate a DDP
Stream. Thus, any of the following fatal errors on a DDP Stream MUST
cause DDP to indicate to the ULP that a fatal error has occurred:

* Underlying LLP Connection or LLP Stream is lost.

* Underlying LLP reports a fatal error.

* DDP Header has one or more invalid fields.

If the LLP indicates to the ULP that a fatal error has occurred, the
DDP layer SHOULD report the error to the ULP (see Section 7.2, DDP
Error Numbers) and complete all outstanding ULP requests with an
error. If the underlying LLP Stream is still intact, DDP SHOULD
continue to allow the ULP to transfer additional DDP Messages on the
outgoing half connection after the fatal error was indicated to the
ULP. This enables the ULP to transfer an error syndrome to the
Remote Peer. After indicating to the ULP a fatal error has occurred,
the DDP Stream MUST NOT be terminated until the Local Peer ULP
indicates to the DDP layer that the DDP Stream should be abortively
torn down.

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RFC 5041 DDP Protocol Specification October 2007

7. Error Semantics

All LLP errors reported to DDP SHOULD be passed up to the ULP.

7.1. Errors Detected at the Data Sink

For non-zero-length Untagged DDP Segments, the DDP Segment MUST be
validated before Placement by verifying:

1. The QN is valid for this stream.

2. The QN and MSN have an associated buffer that allows Placement of
the payload.

Implementers' note: DDP implementations SHOULD consider lack of
an associated buffer as a system fault. DDP implementations MAY
try to recover from the system fault using LLP means in a ULP-
transparent way. DDP implementations SHOULD NOT permit system
faults to occur repeatedly or frequently. If there is not an
associated buffer, DDP implementations MAY choose to disable the
stream for the reception and report an error to the ULP at the
Data Sink.

3. The MO falls in the range of legal offsets associated with the
Untagged Buffer.

4. The sum of the DDP Segment payload length and the MO falls in the
range of legal offsets associated with the Untagged Buffer.

5. The Message Sequence Number falls in the range of legal Message
Sequence Numbers, for the queue defined by the QN. The legal
range is defined as being between the MSN value assigned to the
first available buffer for a specific QN and the MSN value
assigned to the last available buffer for a specific QN.

Implementers' note: for a typical Queue Number, the lower limit
of the Message Sequence Number is defined by whatever DDP
Messages have already been completed. The upper limit is defined
by however many message buffers are currently available for that
queue. Both numbers change dynamically as new DDP Messages are
received and completed, and new buffers are added. It is up to
the ULP to ensure that sufficient buffers are available to handle
the incoming DDP Segments.

For non-zero-length Tagged DDP Segments, the segment MUST be
validated before Placement by verifying:

1. The STag is valid for this stream.

Shah, et al. Standards Track [Page 24]

RFC 5041 DDP Protocol Specification October 2007

2. The STag has an associated buffer that allows Placement of the
payload.

3. The TO falls in the range of legal offsets registered for the
STag.

4. The sum of the DDP Segment payload length and the TO falls in the
range of legal offsets registered for the STag.

5. A 64-bit unsigned sum of the DDP Segment payload length and the
TO does not wrap.

If the DDP layer detects any of the receive errors listed in this
section, it MUST cease placing the remainder of the DDP Segment and
report the error(s) to the ULP. The DDP layer SHOULD include in the
error report the DDP Header, the type of error, and the length of the
DDP segment, if available. DDP MUST silently drop any subsequent
incoming DDP Segments. Since each of these errors represents a
failure of the sending ULP or protocol, DDP SHOULD enable the ULP to
send one additional DDP Message before terminating the DDP Stream.

7.2. DDP Error Numbers

The following error numbers MUST be used when reporting errors to the
ULP. They correspond to the checks enumerated in section 7.1. Each
error is subdivided into a 4-bit Error Type and an 8-bit Error Code.

Error Error
Type Code Description
----------------------------------------------------------
0x0 0x00 Local Catastrophic

0x1 Tagged Buffer Error
0x00 Invalid STag
0x01 Base or bounds violation
0x02 STag not associated with DDP Stream
0x03 TO wrap
0x04 Invalid DDP version

0x2 Untagged Buffer Error
0x01 Invalid QN
0x02 Invalid MSN - no buffer available
0x03 Invalid MSN - MSN range is not valid
0x04 Invalid MO
0x05 DDP Message too long for available buffer
0x06 Invalid DDP version

0x3 Rsvd Reserved for the use by the LLP

Shah, et al. Standards Track [Page 25]

RFC 5041 DDP Protocol Specification October 2007

8. Security Considerations

This section discusses both protocol-specific considerations and the
implications of using DDP with existing security mechanisms. The
security requirements for the DDP implementation are provided at the
end of the section. A more detailed analysis of the security issues
around the implementation and the use of the DDP can be found in
[RDMASEC].

The IPsec requirements for RDDP are based on the version of IPsec
specified in RFC 2401 [IPSEC] and related RFCs, as profiled by RFC
3723 [RFC3723], despite the existence of a newer version of IPsec
specified in RFC 4301 [RFC4301] and related RFCs [RFC4303],
[RFC4306]. One of the important early applications of the RDDP
protocols is their use with iSCSI [iSER]; RDDP's IPsec requirements
follow those of IPsec in order to facilitate that usage by allowing a
common profile of IPsec to be used with iSCSI and the RDDP protocols.
In the future, RFC 3723 may be updated to the newer version of IPsec;
the IPsec security requirements of any such update should apply
uniformly to iSCSI and the RDDP protocols.

8.1. Protocol-Specific Security Considerations

The vulnerabilities of DDP to active third-party interference are no
greater than any other protocol running over transport protocols such
as TCP and SCTP over IP. A third party, by injecting spoofed packets
into the network that are Delivered to a DDP Data Sink, could launch
a variety of attacks that exploit DDP-specific behavior. Since DDP
directly or indirectly exposes memory addresses on the wire, the
Placement information carried in each DDP Segment must be validated,
including invalid STag and octet-level granularity base and bounds
check, before any data is Placed. For example, a third-party
adversary could inject random packets that appear to be valid DDP
Segments and corrupt the memory on a DDP Data Sink. Since DDP is IP
transport protocol independent, communication security mechanisms
such as IPsec [IPSEC] may be used to prevent such attacks.

8.2. Association of an STag and a DDP Stream

There are several mechanisms for associating an STag and a DDP
Stream. Two required mechanisms for this association are a
Protection Domain (PD) association and a DDP Stream association.

Under the Protection Domain (PD) association, a unique Protection
Domain Identifier (PD ID) is created and used locally to associate an
STag with a set of DDP Streams. Under this mechanism, the use of the
STag is only permitted on the DDP Streams that have the same PD ID as
the STag. For an incoming DDP Segment of a Tagged DDP Message on a

Shah, et al. Standards Track [Page 26]

RFC 5041 DDP Protocol Specification October 2007

DDP Stream, if the PD ID of the DDP Stream is not the same as the PD
ID of the STag targeted by the Tagged DDP Message, then the DDP
Segment is not Placed, and the DDP layer MUST surface a local error
to the ULP. Note that the PD ID is locally defined and cannot be
directly manipulated by the Remote Peer.

Under the DDP Stream association, a DDP Stream is identified locally
by a unique DDP Stream identifier (ID). An STag is associated with a
DDP Stream by using a DDP Stream ID. In this case, for an incoming
DDP Segment of a Tagged DDP Message on a DDP Stream, if the DDP
Stream ID of the DDP Stream is not the same as the DDP Stream ID of
the STag targeted by the Tagged DDP Message, then the DDP Segment is
not Placed and the DDP layer MUST surface a local error to the ULP.
Note that the DDP Stream ID is locally defined and cannot be directly
manipulated by the Remote Peer.

A ULP SHOULD associate an STag with at least one DDP Stream. DDP
MUST support Protection Domain association and DDP Stream association
mechanisms for associating an STag and a DDP Stream.

8.3. Security Requirements

[RDMASEC] defines the security model and general assumptions for
RDMAP/DDP. This subsection provides the security requirements for
the DDP implementation. For more details on the type of attacks,
type of attackers, trust models, and resource sharing for the DDP
implementation, the reader is referred to [RDMASEC].

DDP has several mechanisms that deal with a number of attacks. These
attacks include, but are not limited to:

1. Connection to/from an unauthorized or unauthenticated endpoint.
2. Hijacking of a DDP Stream.
3. Attempts to read or write from unauthorized memory regions.
4. Injection of RDMA Messages within a stream on a multi-user
operating system by another application.

DDP relies on the LLP to establish the LLP Stream over which DDP
Messages will be carried. DDP itself does nothing to authenticate
the validity of the LLP Stream of either of the endpoints. It is the
responsibility of the ULP to validate the LLP Stream. This is highly
desirable due to the nature of DDP.

Shah, et al. Standards Track [Page 27]

RFC 5041 DDP Protocol Specification October 2007

Hijacking of an DDP Stream would require that the underlying LLP
Stream is hijacked. This would require knowledge of Advertised
Buffers in order to directly Place data into a user buffer.
Therefore, this is constrained by the same techniques mentioned to
guard against attempts to read or write from unauthorized memory
regions.

DDP does not require a node to open its buffers to arbitrary attacks
over the DDP Stream. It may access ULP memory only to the extent
that the ULP has enabled and authorized it to do so. The STag access
control model is defined in [RDMASEC]. Specific security operations
include:

1. STags are only valid over the exact byte range established by the
ULP. DDP MUST provide a mechanism for the ULP to establish and
revoke the TO range associated with the ULP Buffer referenced by
the STag.
2. STags are only valid for the duration established by the ULP.
The ULP may revoke them at any time, in accordance with its own
upper layer protocol requirements. DDP MUST provide a mechanism
for the ULP to establish and revoke STag validity.
3. DDP MUST provide a mechanism for the ULP to communicate the
association between a STag and a specific DDP Stream.
4. A ULP may only expose memory to remote access to the extent that
it already had access to that memory itself.
5. If an STag is not valid on a DDP Stream, DDP MUST pass the
invalid access attempt to the ULP. The ULP may provide a
mechanism for terminating the DDP Stream.

Further, DDP provides a mechanism that directly Places incoming
payloads in user-mode ULP Buffers. This avoids the risks of prior
solutions that relied upon exposing system buffers for incoming
payloads.

For the DDP implementation, two components MUST be provided: an
RDMA-enabled NIC (RNIC) and a Privileged Resource Manager (PRM).

8.3.1. RNIC Requirements

The RNIC MUST implement the DDP wire Protocol and perform the
security semantics described below.

1. An RNIC MUST ensure that a specific DDP Stream in a specific
Protection Domain cannot access an STag in a different Protection
Domain.

2. An RNIC MUST ensure that if an STag is limited in scope to a
single DDP Stream, no other DDP Stream can use the STag.

Shah, et al. Standards Track [Page 28]

RFC 5041 DDP Protocol Specification October 2007

3. An RNIC MUST ensure that a Remote Peer is not able to access
memory outside the buffer specified when the STag was enabled for
remote access.

4. An RNIC MUST provide a mechanism for the ULP to establish and
revoke the association of a ULP Buffer to an STag and TO range.

5. An RNIC MUST provide a mechanism for the ULP to establish and
revoke read, write, or read and write access to the ULP Buffer
referenced by an STag.

6. An RNIC MUST ensure that the network interface can no longer
modify an Advertised Buffer after the ULP revokes remote access
rights for an STag.

7. An RNIC MUST NOT enable firmware to be loaded on the RNIC
directly from an untrusted Local Peer or Remote Peer, unless the
Peer is properly authenticated (by a mechanism outside the scope
of this specification. The mechanism presumably entails
authenticating that the remote ULP has the right to perform the
update), and the update is done via a secure protocol, such as
IPsec.

8.3.2. Privileged Resources Manager Requirement

The PRM MUST implement the security semantics described below.

1. All Non-Privileged ULP interactions with the RNIC Engine that
could affect other ULPs MUST be done using the Privileged
Resource Manager as a proxy.

2. All ULP resource allocation requests for scarce resources MUST
also be done using a Privileged Resource Manager.

3. The Privileged Resource Manager MUST NOT assume different ULPs
share Partial Mutual Trust unless there is a mechanism to ensure
that the ULPs do indeed share partial mutual trust.

4. If Non-Privileged ULPs are supported, the Privileged Resource
Manager MUST verify that the Non-Privileged ULP has the right to
access a specific Data Buffer before allowing an STag for which
the ULP has access rights to be associated with a specific Data
Buffer.

5. The Privileged Resource Manager SHOULD prevent a Local Peer from
allocating more than its fair share of resources. If an RNIC
provides the ability to share receive buffers across multiple DDP
Streams, the combination of the RNIC and the Privileged Resource

Shah, et al. Standards Track [Page 29]

RFC 5041 DDP Protocol Specification October 2007

Manager MUST be able to detect if the Remote Peer is attempting
to consume more than its fair share of resources so that the
Local Peer can apply countermeasures to detect and prevent the
attack.

8.4. Security Services for DDP

DDP uses IP-based network services; therefore, all exchanged DDP
Segments are vulnerable to spoofing, tampering and information
disclosure attacks. If a DDP Stream may be subject to impersonation
attacks, or stream hijacking attacks, it is highly RECOMMENDED that
the DDP Stream be authenticated, integrity protected, and protected
from replay attacks. It MAY use confidentiality protection to
protect from eavesdropping.

8.4.1. Available Security Services

IPsec can be used to protect against the packet injection attacks
outlined above. Because IPsec is designed to secure arbitrary IP
packet streams, including streams where packets are lost, DDP can run
on top of IPsec without any change.

DDP security may also profit from SSL or TLS security services
provided for TCP or SCTP based ULPs [TLS] as well as from DTLS [DTLS]
security services provided beneath the transport protocol. See
[RDMASEC] for further discussion of these approaches and the
rationale for selection of IPsec security services for the RDDP
protocols.

8.4.2. Requirements for IPsec Services for DDP

IPsec packets are processed (e.g., integrity checked and possibly
decrypted) in the order they are received, and a DDP Data Sink will
process the decrypted DDP Segments contained in these packets in the
same manner as DDP Segments contained in unsecured IP packets.

The IP Storage working group has defined the normative IPsec
requirements for IP Storage [RFC3723]. Portions of this
specification are applicable to the DDP. In particular, a compliant
implementation of IPsec services MUST meet the requirements as
outlined in Section 2.3 of [RFC3723]. Without replicating the
detailed discussion in [RFC3723], this includes the following
requirements:

1. The implementation MUST support IPsec ESP [RFC2406], as well as
the replay protection mechanisms of IPsec. When ESP is utilized,
per-packet data origin authentication, integrity, and replay
protection MUST be used.

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RFC 5041 DDP Protocol Specification October 2007

2. It MUST support ESP in tunnel mode and MAY implement ESP in
transport mode.

3. It MUST support IKE [RFC2409] for peer authentication,
negotiation of security associations, and key management, using
the IPsec DOI [RFC2407].

4. It MUST NOT interpret the receipt of an IKE delete message as a
reason for tearing down the DDP stream. Since IPsec acceleration
hardware may only be able to handle a limited number of active
IPsec Security Associations (SAs), idle SAs may be dynamically
brought down and a new SA be brought up again, if activity
resumes.

5. It MUST support peer authentication using a pre-shared key, and
MAY support certificate-based peer authentication using digital
signatures. Peer authentication using the public key encryption
methods [RFC2409] SHOULD NOT be used.

6. It MUST support IKE Main Mode and SHOULD support Aggressive Mode.
IKE Main Mode with pre-shared key authentication SHOULD NOT be
used when either of the peers uses a dynamically assigned IP
address.

7. Access to locally stored secret information (pre-shared or
private key for digital signing) must be suitably restricted,
since compromise of the secret information nullifies the security
properties of the IKE/IPsec protocols.

8. It MUST follow the guidelines of Section 2.3.4 of [RFC3723] on
the setting of IKE parameters to achieve a high level of
interoperability without requiring extensive configuration.

Furthermore, implementation and deployment of the IPsec services for
DDP should follow the Security Considerations outlined in Section 5
of [RFC3723].

9. IANA Considerations

This document requests no direct action from IANA. The following
consideration is listed here as commentary.

If DDP were enabled a priori for a ULP by connecting to a well-known
port, this well-known port would be registered for the DDP with IANA.
The registration of the well-known port would be the responsibility
of the ULP specification.

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RFC 5041 DDP Protocol Specification October 2007

10. References

10.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.

[RFC2406] Kent, S. and Atkinson, R., "IP Encapsulating Security
Payload (ESP)", RFC 2406, November 1998.

[RFC2407] Piper, D., "The Internet IP Security Domain of
Interpretation of ISAKMP", RFC 2407, November 1998.

[RFC2409] Harkins, D. and Carrel, D., "The Internet Key Exchange
(IKE)", RFC 2409, November 1998.

[RFC3723] Aboba, B., Tseng, J., Walker, J., Rangan, V., Travostino,
F., "Securing Block Storage Protocols over IP", RFC 3723,
April 2004.

[IPSEC] Kent, S. and R. Atkinson, "Security Architecture for the
Internet Protocol", RFC 2401, November 1998.

[MPA] Culley, P., Elzur, U., Recio, R., Bailey, S., and J.
Carrier, "Marker PDU Aligned Framing for TCP
Specification", RFC 5044, October 2007.

[RDMAP] Recio, R., Culley, P., Garcia, D., and J. Hilland, "A
Remote Direct Memory Access Protocol Specification", RFC
5040, October 2007.

[RDMASEC] Pinkerton, J. and E. Deleganes, "Direct Data Placement
Protocol (DDP) / Remote Direct Memory Access Protocol
(RDMAP) Security", RFC 5042, October 2007.

[SCTP] Stewart, R., Ed., "Stream Control Transmission Protocol",
RFC 4960, September 2007.

[SCTPDDP] Bestler, C. and R. Stewart, "Stream Control Transmission
Protocol (SCTP) Direct Data Placement (DDP) Adaptation",
RFC 5043, October 2007.

[TCP] Postel, J., "Transmission Control Protocol", STD 7, RFC
793, September 1981.

Shah, et al. Standards Track [Page 32]

RFC 5041 DDP Protocol Specification October 2007

10.2. Informative References

[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, December 2005.

[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)", RFC
4303, December 2005.

[RFC4306] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol", RFC
4306, December 2005.

[DTLS] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security", RFC 4347, April 2006.

[TLS] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.1", RFC 4346, April 2006.

[iSER] Ko, M., Chadalapaka, M., Hufferd, J., Elzur, U., Shah, H.,
and P. Thaler, "Internet Small Computer System Interface
(iSCSI) Extensions for Remote Direct Memory Access (RDMA)",
RFC 5046, October 2007.

Shah, et al. Standards Track [Page 33]

RFC 5041 DDP Protocol Specification October 2007

Appendix A. Receive Window Sizing

This appendix provides guidance to LLP implementers.

Reliable, sequenced, LLPs include a mechanism to Advertise the amount
of receive buffer space a sender may consume. This is generally
called a "receive window".

DDP allows data to be transferred directly to predefined buffers at
the Data Sink. Accordingly, the LLP receive window size need not be
affected by the reception of a DDP Segment, if that segment is placed
before additional segments arrive.

The LLP implementation SHOULD maintain an Advertised receive window
large enough to enable a reasonable number of segments to be
outstanding at one time. The amount to Advertise depends on the
desired data rate, and the expected or actual round-trip delay
between endpoints.

The amount of actual buffers maintained to "back up" the receive
window is left up to the implementation. This amount will depend on
the rate that DDP Segments can be retired; there may be some cases
where segment processing cannot keep up with the incoming packet
rate. If this occurs, one reasonable way to slow the incoming packet
rate is to reduce the receive window.

Note that the LLP should take care to comply with the applicable
RFCs; for instance, for TCP, receivers are highly discouraged from
"shrinking" the receive window (reducing the right edge of the window
after it has been Advertised).

Appendix B. Contributors

Many thanks to the following individuals for their contributions.

John Carrier
Cray Inc.
411 First Avenue S, Suite 600
Seattle, WA 98104-2860
Phone: 206-701-2090
EMail: [email protected]

Hari Ghadia
Gen10 Technology, Inc.
1501 W Shady Grove Road
Grand Prairie, TX 75050
Phone: (972) 301 3630
EMail: [email protected]

Shah, et al. Standards Track [Page 34]

RFC 5041 DDP Protocol Specification October 2007

Caitlin Bestler
Broadcom Corporation
16215 Alton Parkway
Irvine, CA 92619-7013 USA
Phone: +1 (949) 926-6383
EMail: [email protected]

Uri Elzur
Broadcom Corporation
5300 California Avenue
Irvine, CA 92617, USA
Phone: 949.926.6432
EMail: [email protected]

Mike Penna
Broadcom Corporation
16215 Alton Parkway
Irvine, CA 92619-7013 USA
Phone: +1 (949) 926-7149
EMail: [email protected]

Patricia Thaler
Broadcom Corporation
16215 Alton Parkway
Irvine, CA 92619-7013 USA
Phone: +1 (949) 926-8635
EMail: [email protected]

Ted Compton
EMC Corporation
Research Triangle Park, NC 27709 USA
Phone: +1 (919) 248-6075
EMail: [email protected]

Jim Wendt
Hewlett-Packard Company
8000 Foothills Boulevard
Roseville, CA 95747-5668 USA
Phone: +1 (916) 785-5198
EMail: [email protected]

Mike Krause
Hewlett-Packard Company, 43LN
19410 Homestead Road
Cupertino, CA 95014 USA
Phone: +1 (408) 447-3191
EMail: [email protected]

Shah, et al. Standards Track [Page 35]

RFC 5041 DDP Protocol Specification October 2007

Dave Minturn
Intel Corporation
MS JF1-210
5200 North East Elam Young Parkway
Hillsboro, OR 97124 USA
Phone: +1 (503) 712-4106
EMail: [email protected]

Howard C. Herbert
Intel Corporation
MS CH7-404
5000 West Chandler Blvd.
Chandler, AZ 85226 USA
Phone: +1 (480) 554-3116
EMail: [email protected]

Tom Talpey
Network Appliance
1601 Trapelo Road #16
Waltham, MA 02451 USA
Phone: +1 (781) 768-5329
EMail: [email protected]

Dwight Barron
Hewlett-Packard Company
20555 SH 249
Houston, TX 77070-2698 USA
Phone: +1 (281) 514-2769
EMail: [email protected]

Dave Garcia
24100 Hutchinson Rd.
Los Gatos, CA 95033 USA
Phone: +1 (831) 247-4464
Email: [email protected]

Jeff Hilland
Hewlett-Packard Company
20555 SH 249
Houston, TX 77070-2698 USA
Phone: +1 (281) 514-9489
EMail: [email protected]

Barry Reinhold
Lamprey Networks
Durham, NH 03824 USA
Phone: +1 (603) 868-8411
EMail: [email protected]

Shah, et al. Standards Track [Page 36]

RFC 5041 DDP Protocol Specification October 2007

Authors' Addresses

Hemal Shah
Broadcom Corporation
5300 California Avenue
Irvine, CA 92617 USA
Phone: +1 (949) 926-6941
EMail: [email protected]

James Pinkerton
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052 USA
Phone: +1 (425) 705-5442
EMail: [email protected]

Renato Recio
IBM Corporation
11501 Burnett Road
Austin, TX 78758 USA
Phone: +1 (512) 838-1365
EMail: [email protected]

Paul R. Culley
Hewlett-Packard Company
20555 SH 249
Houston, TX 77070-2698 USA
Phone: +1 (281) 514-5543
EMail: [email protected]

Shah, et al. Standards Track [Page 37]

RFC 5041 DDP Protocol Specification October 2007

Full Copyright Statement

Copyright (C) The IETF Trust (2007).

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contained in BCP 78, and except as set forth therein, the authors
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Shah, et al. Standards Track [Page 38]